This invention relates to automated body fluid or blood analysis equipment and more particularly to automated body fluid or blood electrolyte analysis equipment.
The analysis of a number of factors in blood and blood serum in order to obtain a more thorough and complete picture of a person's physical condition has become a standard medical procedure today. Ranking high among the blood constituents analyzed in order to determine general health are the so-called blood electrolytes. Blood electrolytes are extra-cellular ions contained in the blood, the four major extra-cellular ions being sodium, potassium, chloride and bicarbonate. These four are generally measured as a group because of their interrelationship. The measurement results can provide information necessary in order to maintain a proper chemical balance for a patient during intravenous feeding, and in order to ascertain the general health or specific physical problem of a patient because each measurement either provides an indication of specific physical activity or response, or assists in understanding overall physical condition.
Concentration of sodium ions in the blood is one indication of osmotic pressure. If a person's sodium chloride content increases as indicated by an increase of sodium ions, dehydration has occurred.
Concentration of potassium ions is an indicator of cardiac muscle activity. If the potassium concentration is high above the normal limit, this indicates a weak cardiac muscle which can stop at any time. A low potassium concentration indicates excessive cardiac muscle activity which can result in heart fibrillation.
Human blood has an acid base content that must be maintained within predetermined limits in order to support life. An acid alkaline measure of blood is normally defined in terms of pH. The bicarbonate concentration is a good incicator of the blood pH or blood acid-alkaline balance.
Chloride is not a special indicator in and of itself. However, it is necessary in order to obtain a complete electrolyte picture.
The normal ranges of the electrolyte concentrations are:
sodium: 135-148 Meq PA0 potassium: 3.5 -5.3 Meq PA0 chloride: 98 -108 Meq PA0 bicarbonate: 23 -30 Meq
Sodium and potassium are positive ions, while chloride and bicarbonate are negative ions. If typical values were selected for each of the four and the positive ion values and negative ion values summed and then subtracted from one another there would be a difference of 16 .+-.2. This difference is known as the "anion deficit" or "anion gap".
As noted above there is a range of acceptable concentration values for each of the electrolytes. When an electrolyte analysis is performed all four noted electrolytes are measured and the anion gap is calculated. If it is substantially different from the 16.+-.2 noted above and if the electrolyte concentrations are all within or near normal range, a clear indication is provided that there is some problem associated with a particular patient whose blood is analyzed. On the other hand if one concentration value is clearly outside the normal range, all others are within range and the anion gap differs from normal by the variation in the one concentration, all indicators point to the same problem.
Automated systems in use today which measure all four noted electrolyte concentrations have errors of the order of 2 to 3 Meq. in all but the potassium analysis. The resultant total error when all values are added together can be as great as .+-.8 Meq. The magnitude of this error is so great that it seriously detracts from the usefulness of a blood electrolyte analysis, particularly in emergency situations where the analysis must be performed stat.
A number of different tests and test methods may be employed for the determination of each one of the four primary electrolyte concentrations. The nature of the test will determine the accuracy of the result, that is, how close the result is to the correct answer. The specific apparatus used to perform the test will determine the precision or repetitive consistency of the test results. Generally, sodium and potssium can be determined simultaneously and in one test by use of a flame photometer. Current day photometers employ a known concentration of lithium as a reference in order to ascertain sodium and potassium concentrations. Bicarbonate and chloride concentrations are determined most accurately by a titration method. However, titration methods and apparatus heretofore available for performing titrations do not provide precise results when employed in an automatic apparatus.
The flame photometry procedure and titration procedures available take different periods of time so that if they are employed in an automated testing apparatus, the various tests must be synchronized and the results of each stored and then made available after the completion of the last test. This procedure is cumbersome and time consuming, and may require a memory for storage of the test results from the various tests until the entire testing procedure has been completed. It is desirable to reduce the complexities of such structures and eliminate any memory storage of test results. It is also desirable to perform the tests as quickly as possible in order to satisfy emergency conditions, and to provide the results simultaneously in order to allow immediate calculation of the anion gap and analysis of the patient's blood.